qpnp-smbcharger: Publish charger voltage to the usb psy

Since N, the Keyguard uses watt data rather than amperage alone. It
needs both voltage and amperage information for the power supply
subsystem to do so.

This brings back the "Charging slowly", "Charging" and "Charging
rapidly" texts on the lock screen.

Change-Id: Iac37d8b69d2acc048e8c132b2c26c2bed3676d75